Some Recent Aspects in the Structure Elucidation of Natural Products

Abstract

Abstract-Although in the past 20 yr a large number of new synthetic approaches have been developed methods of isolation and structural elucidation have changed more dramatically in the last two decades than have those of synthesis. For the purification of natural products more and more different Chromatographie techniques like paper, thin-layer, column, and gas-liquid chromatography are being used. Characterizations of natural products by eiemental analysis, melting points, optical rotation values, and degradation and derivatization reactions are being increasingly supported by parameters of spectroscopic tools like proton nudear magnetic resonance, carbon nuclear magnetic resonance, phosphorus nuclear magnetic resonance, fluorine nuclear magnetic resonance, infrared spectroscopy, Raman spectroscopy, absorption spectroscopy, optical rotatory dispersion, circular dichroism, magnetic circular dichroism and computer analysis.The principle of one of the most eflicient methods for the structural elucidation of natural products, pulse Fourier transform "C NMR spectroscopy, is discussed in detail. The usefulness of this method is demonstrated using examples from the peptide, carbohydrate and terpenoid field. The structural elucidations by the application of different physicochemical tools for the three following most recently isolated natural products are given: Hypothalamusreleasing hormones, terpenoids from Me/ia azadirachta Linn., and substances, isolated from urines of sick children.

Mass spectrometry and NMR spectroscopy: modern high-end detectors for high resolution separation techniques – state of the art in natural product HPLC-MS, HPLC-NMR, and CE-MS hyphenations

“…content allows quantication of analytes in investigated specimens. 7 If the identity of an analyte has to be deduced, a maximum of structure related information has to be gained from the detector readout 8,9 to ensure a proper structure elucidation. 10 If qualitative information is to be retrieved, i.e.…”

Nuclear Magnetic Resonance of Small Molecules in Natural Products

“…Since more than four decades (Voelter, 1978), NMR spectroscopy is definitively a key instrumental analysis technique in natural product chemistry, especially if small (<2000 Da) organic molecules are involved. Generally, identification and characterization of such analytical entities is a pivotal prerequisite in many analysis approaches used in natural product research setups.…”